Role of glutamine synthetase activity in the urea regulation of heterocyst and nitrogenase formation in the cyanobacterium Anabaena cycadeae

✍ Scribed by Surendra Singh; P. S. Bisen

• Publisher: John Wiley and Sons
• Year: 1994
• Tongue: English
• Weight: 360 KB
• Volume: 34
• Category: Article
• ISSN: 0233-111X
• DOI: 10.1002/jobm.3620340309

✦ Synopsis

Abstract

Growth and urea regulation of heterocyst and nitrogenase formation have been studied in the diazotrophic cyanobacterium Anabaena cycadeae and its glutamine auxotrophic mutant strain lacking glutamine synthetase (GS) activity. The parent strain having normal GS activity utilized urea as sole nitrogen source without producing N~2~‐fixing heterocysts. In contrast, the mutant strain lacking GS activity could not utilize urea as sole nitrogen source although similar to the parent strain it lacked N~2~‐fixing heterocysts in urea‐medium. Both parent and mutant strain showed high levels of urea uptake and urease activity in the presence and absence of a GS inhibitor, l‐methionine‐dl‐sulphoximine (MSX). Urea‐dependent NH production by MSX‐untreated cells was only confined to the mutant strain lacking GS activity whereas the parent strain having normal GS activity produced NH only in the presence of MSX. These results suggest that (i) GS is the sole NH assimilating as well as glutamine‐forming route in heterocystous N~2~‐fixing cyanobacteria; (ii) while GS activity is necessarily required for the assimilation of urea as sole nitrogen source, it is however, not required for the urea inhibition of heterocysts and nitrogenase formation; (iii) that NH resulting from the hydrolysis of urea and not GS‐mediated pathway of NH assimilation appears to be the initial repressor signal for heterocysts and nitrogenase formation; and (iv) GS does not control the formation of N~2~‐fixing heterocysts, urea uptake and urease activity systems.